I have an old Colt 3/4 circle semi bolt carrier.  Is there anything wrong with using it?  I am not using it for heavy loads, just plain 55gr fodder.  What is the disadvantage with this type of carrier, not including the shortened firing pin ramp hood that the new ones have extended like M16 carriers?  Should I dump this carrier and replace it with a full circle semi carrier?  Is it worth it?

It weighs less so it has a higher speed of action but the weight is less so its harder to load rounds by momentum if the chamber is dirty.  In short you will not be able to tell a difference in most situations.  I would not sweat it for everday plinking etc.  It was cut that way to clear the block Colt puts in the lower and be semi auto compliant.

wrong on clearing the sear block............a regular AR-15 carrier will work fine in a colt sear block lower.  the sear block will not allow you to use a DIAS, an M16 bolt carrier, or required full auto trigger pieces.

the cutaway bolt carrier from my understanding is to eliminate the use of devices such as the lightning link for full auto conversions